Caliper guide assembly

ABSTRACT

A caliper guide assembly for a heavy vehicle disc brake. The caliper guide assembly may include a wear sensor arranged to detect the position of a guide pin in relation to a guide bore. The guide pin and a guide surface may have different cross sectional profiles to define at least one void therebetween. The wear sensor may be at least partially accommodated within the void.

TECHNICAL FIELD

The present invention relates to a disc brake and particularly but not exclusively to a guide assembly for slidably mounting a caliper of a disc brake, and may incorporate a wear sensor.

BACKGROUND

Disc brakes are commonly used for braking heavy vehicles such as trucks, buses and coaches.

Disc brakes conventionally comprise a brake carrier and a caliper. The brake carrier is arranged to carry brake pads on each side of a rotor. The caliper is slidably mounted on the brake carrier by two or more guide assemblies, such that when the disc brake is actuated, the caliper is able to slide with respect to the brake carrier so that both brake pads are urged onto a rotor in a clamping action to effect braking.

A guide assembly typically comprises a guide pin along which the caliper can slide, and a bore disposed in the caliper for receiving the guide pin.

To achieve free sliding of the caliper in a broad range of operating conditions, the guide assemblies must take account of manufacturing tolerances, effects of heating or cooling in use, and accommodate deflections of the disc brake due to the braking torque.

In addition, it is desirable for the vehicle operator to be provided with the wear status of the brake pad friction material in order to be notified when brake pads are to be changed, to maintain safe operation of the disc brake. However, known wear sensing arrangements may be costly and can restrict the design of other parts of the brake. Further, known arrangements may be susceptible to environmental contamination and damage.

SUMMARY

The present invention seeks to alleviate the problems associated with the prior art.

Accordingly, a first aspect of the invention provides a caliper guide assembly for a heavy vehicle disc brake. The caliper guide assembly comprising: a guide pin having a guide portion, a guide bore having a guide surface arranged to receive the guide portion and permit relative axial sliding thereof, and a wear sensor arranged to detect the position of the guide pin in relation to the guide bore, wherein a void is provided radially between the guide portion and the guide bore and the wear sensor is at least partially accommodated within the void.

Advantageously, this arrangement enables otherwise redundant space in the disc brake to be used for wear sensing. Further the space is well protected from the surrounding environment.

Optionally, the guide portion and the guide surface have different cross-sectional profiles to define the void along at least part of their length.

Optionally, the guide surface has a non-circular, preferably substantially constant cross section.

Advantageously, it has been found generally easier to manufacture a guide surface that is non-circular rather than a non-circular pin.

Optionally, the guide surface has an oval cross section.

Advantageously, an oval cross-section has been found effective for smooth guidance whilst providing space for the wear sensor.

Optionally, the guide pin has a substantially circular, preferably substantially constant outer profile.

Advantageously, this arrangement has been found simple to manufacture.

Optionally, the bore is a through bore and the assembly further comprises a cover to close one opening of the through bore and wherein the wear sensor is optionally mounted to the cover.

Advantageously the cover inhibits the contamination of the guide assembly and wear sensor and by optionally mounting the wear sensor to the cover, fitting and removal of the sensor may be simplified, and the cover may provide a secure mounting.

Optionally, the sensor comprises a portion overmolded or at least partially encapsulated into the cover.

Advantageously, this is an effective way of manufacturing the cover whilst also protecting the sensor.

Optionally, the wear sensor extends from the cover into the void in a self-supporting manner.

Optionally, the guide surface is a surface of a bush separately mounted to the bore.

Advantageously, using a bush allows suitable guide material to be used that may differ from that of the brake caliper. If the guide surface has a non-circular inner profile, manufacturing this in a bush may simplify its shaping.

Optionally, the bore is provided in a caliper of a heavy vehicle disc brake.

Advantageously, providing the bore in the caliper may permit a more compact brake to be achieved compared to providing it in the carrier.

Optionally, the guide pin further comprises a mounting portion configured for mounting to a brake carrier of a heavy vehicle disc brake.

Optionally, the sensor is a Hall Effect sensor or an optical sensor.

Advantageously, both of these types of sensor are compact, inexpensive and reliable.

A second aspect of the present invention provides a disc brake incorporating a caliper guide assembly according to the first aspect of the present invention.

Optionally, the heavy vehicle disc brake further comprises a second caliper guide assembly.

Optionally, the second caliper guide assembly comprises a second guide pin having a second guide portion and a second guide bore having a second guide surface, wherein the second guide portion and a second guide surface have substantially the same cross-sectional profiles.

A third aspect of the present invention provides a caliper guide assembly for a heavy vehicle disc brake. The caliper guide assembly comprising: a guide pin having a guide portion, a guide bore having a guide surface arranged through to receive the guide portion and permit relative axial sliding thereof, and a wear sensor arranged to detect the position of the guide pin in relation to the guide bore, wherein a void accessible from an opening of the guide bore is provided within the assembly and the wear sensor is at least partially located within the void.

Optionally, the void may be at least partially provided within a recess of the guide pin.

Advantageously, this permits additional space to accommodate the sensor.

Optionally, the sensor directly senses the position of the guide pin with respect to the sensor.

Advantageously, this arrangement avoids the need for additional components, such as magnets that interact within the sensor.

A fourth aspect of the present invention provides a wear sensor for use in a caliper guide assembly, the wear sensor comprising a probe configured to extend into a void between a guide pin and a bore of the caliper guide assembly.

Optionally, the wear sensor is arranged to mount to an inboard end of the bore, and the probe is arranged to extend outboard therefrom.

Optionally, the wear sensor is mounted to a cap arranged to close an inboard end of the bore.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is an isometric view of a disc brake having the guide assembly of a first embodiment and second embodiment of the present invention;

FIG. 2 is a plan cross-sectional view of the guide assemblies shown in FIG. 1 on a plane through the center of both guide assemblies with the caliper in a position with the brake pads unworn;

FIG. 3 shows an isometric view of the same cross-section as FIG. 2;

FIG. 4 shows the same cross-sectional view as FIG. 2, but with the brake pads worn;

FIG. 5 shows an isometric, cross-sectional view the same as FIG. 3, but with the brake pads worn;

FIG. 6 shows an enlarged cross-sectional view of the guide assembly of the first embodiment of the present invention;

FIG. 7 shows an enlarged cross-sectional view of the guide assembly on the plane 6-6;

FIG. 8 shows an exploded cross-sectional view of the guide assembly of the first embodiment of the present invention; and

FIG. 9 is an enlarged cross-sectional view of the guide assembly of the second embodiment of the present invention.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

FIG. 1 depicts an embodiment of a disc brake 8. The disc brake comprises a caliper 20 slidably mounted with respect to a brake carrier 30 by two guide pin assemblies. The caliper 20 has a housing 22 typically formed from cast iron or steel. The brake carrier 30 is typically also formed from cast iron or steel.

The brake carrier 30 carries an inboard brake pad 50 a and an outboard brake pad 50 b. A rotor 40 (see FIG. 2), rotatable about an axis extending in the axial direction A, is positioned between the brake pads. An air actuator (not shown) is provided to move the inboard brake pad 50 a into frictional contact with the rotor via an actuation mechanism (not shown) housed within the caliper housing 22 and which acts on the inboard brake pad 50 a. When the inboard brake pad 50 a is pushed towards and contacts the rotor, the caliper 20 is then caused to slide inboard along first and second caliper guide assemblies 10 a and 10 b.

As the caliper 20 slides inboard, it moves the outboard brake pad 50 b towards the rotor 40. Hence, the rotor 40 becomes clamped between the inboard and outboard brake pads and the rotation of the rotor is frictionally inhibited.

So as to minimize the potential for the sliding of the caliper 20 to be prevented or restricted due to jamming or binding of the guide assemblies caused by thermal expansion, deflection under load, wear or the like, the first guide assembly 10 a has a void to allow for free running of the guide assemblies even if the guide assembly is not in its nominal position. The first guide assembly 10 a is a guide assembly according to a first embodiment of the present invention.

The second guide assembly 10 b is longer than the first and comprises a circular guide bush and a complementary circular guide sleeve. The second guide assembly 10 b is a guide assembly according to a second embodiment of the present invention. Although the disc brake 8 is shown with guide assemblies according to both a first and second embodiment of the present invention, in practice a disc brake would typically be fitted with either one or the other guide assemblies of the present invention and the other assembly would be conventional.

With reference to FIGS. 2, 3 and 6 the first guide assembly 10 a, comprises a bore 12 a extending parallel to axis A through the housing 22. The bore 12 a has a circular cross-sectional profile to receive a guide pin 11 a and at least one guide bush 13 a with a circular outer profile and a non-circular, e.g., oval, inner profile to guide the guide pin within the bore.

The guide pin 11 a comprises a fastener to secure the guide pin to the brake carrier 30. In this first embodiment the fastener is a bolt 14 a that affixes to the brake carrier 30 by screwing into a threaded bore in the brake carrier.

With particular reference to FIG. 6, the guide pin 11 a further comprises a guide sleeve 15 a at least substantially surrounding the fastener and over which the caliper 20 slides. The sleeve is a hollow tube with a substantially circular cross-sectional profile. The head of the central bore of the sleeve is stepped so that the bolt 14 a is able to hold the sleeve in place when tightened on to the brake carrier 30.

The bore 12 a of the guide assembly 10 a is an elongate hole extending from a first side (inboard) to the second side (outboard) of the caliper housing 22. The caliper 20 is slidably mounted with respect to the brake carrier 30 by sliding the guide pin 11 a through the bore 12 a. Hence, when the disc brake is actuated, the caliper 20 is able to slide in the axial direction A along the guide pin 11 a.

The guide bush 13 a is configured to form a close fit with the bore 12 a and act as an inner liner in the bore. For heavy vehicle applications the internal diameter of the bush members is typically in a range of 25-40 mm. As can be seen in FIG. 2, the guide bush 13 a does not extend the full depth of the bore 12 a.

The guide bush 13 a may be manufactured from steel, bronze, plastic, rubber or a composite of any of these, and may include a low friction coating such as PTFE. The guide bush 13 a may have a plain inner surface or a suitable pattern of depressions to assist in the sliding of the caliper and the retention of lubricants. A convoluted bellows type seal 17 (FIG. 8) encircles the guide pin 11 a and connects to the brake carrier 30 and brake caliper 20 to protect the first guide assembly 10 a from contamination.

The diameter of the guide pin 11 a is selected to correspond to the smallest diameter of the guide bush 13 a. Accordingly, the clearance between the guide pin 11 a and the guide bush 13 a in the tangential direction Y is minimal and so vibration, noise, stress and excess wear are reduced. The largest diameter of the bush provides a greater clearance between the guide pin and the bush in the circumferential direction X to allow for a predetermined amount of play to accommodate manufacturing tolerances, heat expansion and brake torque induced deflection.

With particular reference to FIGS. 6, 7 and 8, a wear sensor of the first embodiment of the present invention will now be discussed in more detail.

In order to inhibit the contamination of the first guide assembly 10 a with foreign matter, a cap or cover 60 a closes the inboard end of the bore 12 a. Conventionally, covers used for this purpose are formed from metal and press fitted into the end of the bore 12 a.

However, in this embodiment, the cover 60 a is combined with a wear sensor 62 a. As a result, construction of the cover 60 a differs somewhat from conventional covers as discussed below. In this embodiment, the cover 60 a continues to comprise a cap portion 64 a that has a circular end face to close off the bore and a skirt portion arranged to extend inboard and frictionally engage the surface of the bore 12 a.

However, in this embodiment, the cap portion 64 a is formed from plastics resin material and is manufactured e.g., to overmold and at least partially encapsulate components of the wear sensor 62 a. Specifically, in this embodiment the cap portion 64 a partially encapsulates first and second sensor probes 66 at an inboard end of each probe, such that the probes extend outboard therefrom parallel to the axis A-A. In addition, the cap portion 64 a encapsulates a signal processing part 68 of the wear sensor 62 a. In this embodiment the signal processing part 68 projects inboard and is accommodated within a recess at the head of the bolt 14 a.

Finally, the cap portion 64 a also mounts a connector portion 70 a of the wear sensor 62 a on an inboard face of the cap portion 64 a. The connector portion 70 a provides in this embodiment a suitable connector such as a plug or socket for a cable that is arranged to extend to the vehicle (not shown) in which the disc brake is fitted. This enables the vehicle to provide an indication to a vehicle operator of the state of wear of the brake pads 50 a and 50 b, e.g., via a display on a dashboard of the vehicle, or some other form of audio/visual indicator.

As can be seen clearly in FIGS. 6 and 7, the probes 66 extend outboard into the void provided between the guide pin 11 a and guide bush 13 a by virtue of the oval shaped inner profile of the guide bush. As such, the probes 66 extend alongside the guide sleeve 15 a of the guide pin 11 a and, as the friction material of the brake pads 50 a and 50 b wears away during usage of the disc brake 8, the relative position of the probes 66 with respect to the guide sleeve 15 a changes. This may be seen by comparing the position of the probes 66 with respect to the guide sleeve 15 a in FIGS. 2 and 3 which the friction material on the brake pads 50 a and 50 b is unworn, with the position in FIGS. 4 and 5 in which the friction material is substantially fully worn and the probes 66 have moved inboard by a distance equivalent to the cumulative wear of the friction material of the outboard pad 50 b and any additional wear of material from the outboard face of the brake rotor 40.

In a preferred embodiment, the wear sensor 62 a is a Hall Effect sensor and since the guide sleeve 15 a is metallic the relative movement of the probes 66 with respect to the guide sleeve 15 a results in a signal from the probes which can be used to derive the relative movement of probe and sleeve, and thereby the wear of the friction material.

In other embodiments, the sensor may be any other suitable sensor, such as an optical sensor. Further, the sensor probes may be embedded within the guide bush 13 a, or specific recesses provided in the bush to accommodate the probes without the clearance between bush and sleeve being reduced by virtue of the presence of the probes. In further embodiments, if elastomeric, e.g., synthetic rubber bushes are used, the probes may be molded (encapsulated) into the bush to provide the void. In certain embodiments, the signal processing portion and/or connector portion may further be integrated into the bush rather than to the cover 60 a. Further, the cover, bush and sensor may all be provided as a single component. In alternate embodiments, only a single probe or more than two probes may be used, and the signal processing portion may be omitted. The connector may be replaced by a cable arranged to extend to a remote location, e.g., on the vehicle.

Referring to FIG. 2, in a second embodiment of the present invention, the wear sensor is instead provided on the second guide assembly 10 b, which has a guide bush 13 b.

As noted above, the second guide pin 11 b is longer than the first guide pin 11 a. However, both guide pins use bolts of the same length. This means that the sleeve 15 b of the second guide assembly 10 b has a significant void inboard of the head of the bolt 14 b. The void is defined by the head of the bolt 14 b, inboard portion of the sleeve 15 b, and cap portion 64 b of the cover 60 b (see FIG. 9). In this embodiment, this void is utilized to provide space both for a sensor probe 66 b that extends parallel to axis A-A proximate to the inboard end of sleeve 15 b, as well as the signal processing portion 68 b of the wear sensor 62 b.

As in the first embodiment, the cap portion 64 b is formed from a suitable plastics resin material and the sensor probe 66 b, signal processing portion 68 b and connector portion 70 b are all preferably integrally molded to be at least partially encapsulated within the resin of the cap portion 64 b. As in the first embodiment, the wear sensor 62 b is preferably a Hall Effect type sensor and the relative movement of the sensor probe 66 b to the second guide pin 11 b, and in particular the sleeve 15 b thereof, causes the readings in the wear sensor 62 b to change, and therefore the wear of the friction material of the outboard brake pad 50 b to be derived therefrom. It should be noted that by mounting the probe proximate to the sleeve, relative movement of the sensor and sleeve can be detected without additional components such as magnets mounted to the pin.

If the inboard and outboard brake pads wear at a similar rate, and are changed as a pair, the fact that the outboard brake pad has its wear sensed by the sensor of the first embodiment or the second embodiment means that the equivalent wear can be inferred for the inboard brake pad. However, it is contemplated that the sensor described above could be used in conjunction with a further sensor to determine the actual wear on the inboard brake pad. For example, a sensor that monitors the extension of a wear adjustment mechanism of the disc brake could be used to measure total wear of both brake pads and wear of the inboard pad could be calculated from the difference of total wear and outboard brake pad wear.

The embodiments of the guide assembly are suitable for use in any type of disc brake, including pneumatic, hydraulic, electrically and mechanically actuated disc brakes. However, the embodiments are believed to be particularly beneficial in air-actuated disc brakes for heavy commercial vehicles, where rotors typically have a diameter of between 30-60 cm, meaning that the torque and heat effects may be more significant than in hydraulic disc brakes for smaller, lighter vehicles.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. 

What is claimed is:
 1. A caliper guide assembly for a heavy vehicle disc brake, the caliper guide assembly comprising: a guide pin having a guide portion; a guide bore having a guide surface arranged to receive the guide portion and permit relative axial sliding thereof; and a wear sensor arranged to detect a position of the guide pin in relation to the guide bore; wherein a void is provided radially between the guide portion and the guide bore and the wear sensor is at least partially accommodated within the void.
 2. The caliper guide assembly of claim 1 wherein the guide portion and the guide surface have different cross-sectional profiles to define the void along at least part of their length.
 3. The caliper guide assembly of claim 1 wherein the guide surface has a non-circular, preferably substantially constant, cross section.
 4. The caliper guide assembly of claim 3 wherein the guide surface has an oval cross section.
 5. The caliper guide assembly of claim 1 wherein the guide pin has a substantially circular outer profile.
 6. The caliper guide assembly of claim 5 wherein the guide pin has a substantially constant outer profile.
 7. The caliper guide assembly of claim 1 wherein the guide bore is a through bore and the caliper guide assembly further comprises a cover to close one opening of the through bore.
 8. The caliper guide assembly of claim 7 wherein the wear sensor is mounted to the cover.
 9. The caliper guide assembly of claim 7 wherein the wear sensor comprises a portion at least partially encapsulated into the cover.
 10. The caliper guide assembly of claim 7 wherein the wear sensor extends from the cover into the void in a self-supporting manner.
 11. The caliper guide assembly of claim 1 wherein the guide surface is a surface of a bush separately mounted to the guide bore.
 12. The caliper guide assembly of claim 1 wherein the guide bore is provided in a caliper of the heavy vehicle disc brake.
 13. The caliper guide assembly of claim 1 wherein the guide pin further comprises a mounting portion operable to mount the caliper guide assembly to a brake carrier of the heavy vehicle disc brake.
 14. The caliper guide assembly of claim 1 wherein the wear sensor is a Hall Effect sensor.
 15. The caliper guide assembly of claim 1 wherein the wear sensor is an optical sensor.
 16. A heavy vehicle disc brake comprising: a caliper guide assembly that includes: a guide pin having a guide portion; a guide bore having a guide surface arranged to receive the guide portion and permit relative axial sliding thereof; and a wear sensor arranged to detect a position of the guide pin in relation to the guide bore; wherein a void is provided radially between the guide portion and the guide bore and the wear sensor is at least partially accommodated within the void.
 17. The heavy vehicle disc brake of claim 16 wherein the heavy vehicle disc brake further comprises a second caliper guide assembly.
 18. The heavy vehicle disc brake of claim 17 wherein the second caliper guide assembly comprises a second guide pin having a second guide portion and a second guide bore having a second guide surface, wherein the second guide portion and the second guide surface have substantially the same cross-sectional profiles.
 19. A caliper guide assembly for a heavy vehicle disc brake, the caliper guide assembly comprising: a guide pin having a guide portion; a guide bore having a guide surface arranged to receive the guide portion and permit relative axial sliding thereof; and a wear sensor arranged to detect a position of the guide pin in relation to the guide bore; wherein a void accessible from an opening of the guide bore is provided within the caliper guide assembly and the wear sensor is at least partially located within the void.
 20. The caliper guide assembly of claim 19 wherein the guide pin has a recess, and the void is at least partially provided within the recess of the guide pin. 